eLFH - Heat and Temperature Flashcards
Temperature dependent enzymatic reactions mechanism
Increase in temperature leads to reacting molecules gaining kinetic energy
Increases likelihood of collision between enzyme and substrate
Thus increases rate of reaction
Explanation for there being an optimal temperature for temperature dependent enzymatic reactions
There is a temperature at which an enzyme’s catalytic activity is greatest
Above that temperature, enzyme structure begins to denature
Optimal temperature for temperature dependent enzymatic reactions
+ exception to this
37.0 degrees Celsius
Except enzymes in testes which function optimally at slightly lower temperature
Energy definition
Ability to do work
Can be mechanical, chemical, electrical or thermal
Heat (or heat energy) definition
Total energy of molecular motion in a substance
Cannot be directly measured
Heat equation
Equation for Kinetic energy
Kinetic energy = 1/2 Mass x Velocity^2
Factors which Heat / Heat energy depends on
Kinetic energy of molecules of a substance
Physical state of the substance
Number of molecules in the substance (i.e its mass)
Temperature definition
Average kinetic energy of atoms which make up a substance
When temp is measured in Kelvin, it is directly proportional to average kinetic energy of molecules in the substance
Relationship between heat energy and temperature
Temperature is measure of likelihood that one substance will transfer heat energy to another
Eg. Iceberg has higher amount of heat energy than pan of boiling water (due to its mass) but boiling water is higher temperature and would transfer heat energy to iceberg
Specific heat capacity definition
Amount of heat energy required to raise temperature of 1 kg (a unit mass) of a substance by 1 Kelvin (a unit temperature rise)
Specific heat capacity Equation
Units of specific heat capacity
kJ / kg / K
can also be as kcal / kg / K
Conversion of kJ to kcal
1 kcal = 4.18 kJ
Heat capacity definition
Amount of heat energy required to raise the temperature of a given OBJECT by 1 Kelvin
I.e Heat capacity = Specific heat capacity x Mass of object
Units of heat capacity
kJ / K
Heat transfer from one object to another equation
Amount of heat transferred = Mass x Change in temperature x Specific heat capacity
How to calculate temperature change when blood / fluid transfused
Amount of heat gained by infusion = amount of heat lost by body (amount of heat transferred)
Therefore can rearrange equation for new temperature (note change in temperature if temp for warmer object is Old temp - New temp, and for cooler object is New temp - Old temp)
Heat transfer definition
Passage of energy from a warmer object to a cooler object
Methods of heat transfer
Radiation 40%
Convection 30%
Evaporation 20%
Respiration 10%
(Conduction - minimal, 3-5%)
Royal College Exam Room Chat
Reasons for conduction being a limited area of heat loss for patient in operating theatre
Air around patient is poor heat conductor
Table is well insulated
Contact area between patient and table relatively small
Conduction mechanism
Heat transfer due to collision of molecules of two substances
Molecules’ kinetic energy transferred from higher temp substance to lower temp substance
Convection definition
Transfer of heat by circulation through gas or liquid
Convection mechanism with patient in operating room
Patient on table surrounded by air
Air warmed by conduction of heat from patient
As air increases in temp, becomes less dense and rises
Replaced by less dense cooler air
Cycle repeats creating convection current
Continues until equilibrium of temperature reached
How radiation differs from convection and conduction
Does not require matter to transfer heat (eg method of sun heating the earth)
Radiation mechanism
All objects above 0 Kelvin emit radiation as electromagnetic waves
Amount radiation emitted vs absorbed is a function of the object’s temperature
Waves falling within infrared spectrum are felt as heat
Stefan-Boltzmann Law
Relates total amount of radiation emitted by an object to its temperature
Evaporation mechanism of heat loss
Latent heat of vaporisation is taken from body to vaporise water / liquid
Can be described in terms of the other methods of heat loss
E.g Conduction from body to fluid causing evaporation. heat carried away by convection
Evaporation heat loss from patient in theatre
Sweat or antiseptic solution evaporating from skin
Fluid evaporates from exposed moist internal body cavities
Respiration heat loss
8% humidification
2% warming of inspired gases
Occurs via combination of other modes of heat transfer
